"The fusion of seismic and magnetotelluric data holds promise in discriminating between underground nuclear blasts and earthquakes. MT measurements can sense several different effects of nuclear blasts: the acoustic wave which travels slowly away from theblast center, the upward propagating wave which generates Alfv¿n waves, and the direct electromagnetic pulse (EMP) which propagates through the earth's atmosphere after traveling from the buried location to the surface.These signals are mixed in with noise signals which will mask their presence: plane wave ionospheric resonances, and worldwide lightning which can mimic EMPs from explosions. This proposed work will reduce this noise to increase the SNR to detectablelevels, and rule out lightning as the source of the EMP. We will explore the aspect of sensor arrays, beam-forming, and multivariate noise reduction. We will draw on our experience with multivariate algorithms for coherent noise mitigation, and in thelocation of global lightning. A demonstration experiment will validate the concept of using a localized array of sensors in California to derive directional EMP location information, and the identification of plane-wave signals which constitute noise.This experiment will demonstrate the concept of fusing magnetic with seismic data to differentiate between nuclear explosions and earthquakes. This work will demonstrate that important observable electromagnetic phenomena produ